contrib/add_cosigner: document usage process
contrib/add_cosigner: document usage process

wakiyamap/electrum-mona,wakiyamap/electrum-mona,pooler/electrum-ltc,pooler/electrum-ltc,pooler/electrum-ltc,spesmilo/electrum,wakiyamap/electrum-mona,pooler/electrum-ltc,wakiyamap/electrum-mona,spesmilo/electrum,spesmilo/electrum,spesmilo/electrum